IRF axesΒΆ
Most IRFs are dependent on parameters, and the 1-dimensional parameter arrays are stored in columns. The following names are recommended:
- For energy grids, see here
for basic recommendations. Column names should be
ENERGY
orENERG_LO
,ENERG_HI
because that is used (consistently I think) for OGIP and Fermi-LAT. For separate HDUs, the extension names should beENERGIES
orEBOUNDS
(used by Fermi-LAT consistently). - Sky coordinates should be called
RA
,DEC
,GLON
,GLAT
,ALT
,AZ
(see Coordinates) - Field of view coordinates
DETX
,DETY
orTHETA
,PHI
for offset and position angle in the field of view (see Field of view). - Offset wrt. the source position should be called
RAD
(this is what the OGIP PSF formats use).
In the specific case of point-like IRFs:
- The energy-dependent radius of the selected region of interest should be
RAD_MAX
The IRF format specifications mention a recommended axis format and axis units. But tools should not depend on this and instead:
- Use the axis order specified by the
CREF
header keyword (see BINTABLE HDU) - Use the axis unit specified by the
CUNIT
header keywords (see BINTABLE HDU)